1. Field of the Invention
The present invention relates to a method for modeling a ball grid array (BGA) of surface mounted devices and, more particularly, to a method for measuring confidence of a BGA model in semiconductor surface mounted devices.
2. Discussion of Related Art
In chip packaging technology, ‘Ball Grid Array’ (BGA) has been used, particularly, in semiconductor Surface Mounted Devices (SMD). With BGA, more electrical connections between chips and printed circuit boards can be made because the electrical connections are on the under-side of the chip, freeing up more space than the conventional chips having surround edge connections.
There are many ways to inspect the semiconductor Surface Mounted Devices. Among them, inspection by illumination inspection, a low-power lens or stereo microscope and an automated x-ray inspection system are the most common.
A disadvantage of BGA packaging is that visual inspections are difficult because, once the chip is attached to the circuit board, the electrical connections are hidden under the package. Thus, model based techniques are being used and are continually being developed to improve on inspection applications in semiconductor Surface Mounted Devices. The SMD component model in general contains information about the geometric structures and properties of the SMD component. The main advantages of the model based technique for inspection of SMD components are easy adaptability of a SMD model to different imaging sensor parameters, easy modification of the model, and editing capability.
A SMD component model can be generated either from a CAD data file describing the SMD component or from images of the actual SMD component to be tested or inspected. When the CAD data file is not available, the SMD component model is generated using images that are extracted from the SMD component. Typically, one to two images of an actual SMD component are used for modeling the device through image extraction techniques.
Because no geometric description about the SMD component is available before the model generation process, it is difficult to measure the correctness of the modeling results directly by comparing the extracted model to the real component. Therefore, a need exists for modeling precisely the SMD component and obtaining accurate measurements with high level of confidence of the correctness of the model.